Composition of a captured image may be difficult for some users of image capture devices. In addition to lighting, focus, focal length and field-of-view issues, the user must also consider the exposure of the image, referred to hereinafter as tone composition, so that all objects in the image have adequate discernable detail. That is, do the objects of interest and/or the background objects of the captured image have tone composition that is in an interesting and visually pleasing manner? Less than optimal tone composition in a captured image results in portions of the image being overexposed, discernable as very bright or white regions with little visible detail, and/or portions of the image being underexposed, discernable as very dark or black regions with little visible detail.
Images that exhibit a wide range of tones, referred to as high contrast images, are difficult to capture without undesirable overexposed or underexposed regions since the lighting conditions over the frame of the captured image varies over a large range. The exposure of the image is based upon determining a desirable exposure for the primary object of interest in the frame. Accordingly, when the primary object of interest is captured, details of the primary object of interest are discernible. However, when the image is captured in a high contrast image, other objects may be overexposed or underexposed because the exposure has not been optimized for the lighting conditions of these objects, resulting in less discernable detail for these objects.
Ideally, this condition would be noticed by the user, either before the image is taken, or immediately after, allowing another adjusted image to be captured. Digital cameras typically provide a display that provides a preview of the image to be captured and postview of the captured image. However, the displayed image quality and/or resolution on these displays is often inadequate for distinguishing highlight and shadow detail. Such displays may have a very limited contrast range. In addition, some viewing conditions in the field make it difficult to critically evaluate a displayed image since ambient lighting conditions interfere with image viewing. For example, even if the display was capable of displaying images with very high contrast, glare from the scene may limit the discernable contrast of the viewed image.
FIG. 1A is a simplified exemplary high contrast captured image 102 of a scenic mountain 104, with a deer 106 and a tree 108 in the foreground, and clouds 110 in the background. Assuming it is a bright day, the high contrast image 102 shows the clouds as very bright and white, with a more desirable contrast for the deer 106 and tree 108 in the foreground. The image 102 is, to some, not a visually pleasing image because the clouds 110 have little discernable detail, and accordingly, may not be interesting to the viewer. Since the exposure is optimized for the primary objects of interest of the image 102, the scenic mountain 104 with the deer 106 and the tree 108 in the foreground, exposure cannot be optimal for the clouds 110. Accordingly, the clouds 110 are washed out, or overexposed, in the image 102 when captured.
FIG. 1B is a simplified exemplary high contrast captured image 112 of a woman 114. A barely visible picture 116 is in the background of image 112. The image 112 is, to some, not a visually pleasing image because the picture 116 is not visible in the background of the image 112. Since the image 112 was captured indoors under artificial lighting conditions without a flash to provide supplemental lighting to the background, the upper left-hand corner of image 112 appears as a black region 118. That is, the black region is underexposed since there is very little to no lighting of that area, relative to the amount of light detected from the object of interest, the woman 114. Similarly, the gray region 120 illustrates another relatively underexposed area (a heavily shaded area) of the background. The underexposed gray region 120 provides for limited visibility of the left-hand side of image 112. However, underexposed background objects such as the picture 116 are not easily discernible by a viewer.
In the image 102, the clouds 110 are very bright, relative to the scenic mountain 104 with the deer 106 and the tree 108 in the foreground. Accordingly, when the image 102 is captured with the deer 106 and tree 108 set at a middle gray tone setting, the clouds 110 are overexposed. That is, when the image 102 is captured, the pixels of a photoelement array that are detecting light from the clouds 110 become saturated, and thereby record the clouds 110 as being very bright and white.
Similarly, in the image 112, the background area of the image where the picture 116 resides is dark, relative to the image of the woman 114. Accordingly, when the image 112 is captured with the woman 114 set at a middle gray tone setting, the background area where the picture 116 resides is underexposed. That is, when the image 112 is captured, the pixels of a photoelement array that are detecting light from picture 116 and the left-hand side of the image 112 detect relatively little light, and thereby record the picture 116 as being black or shaded. It is therefore desirable to assist a user of a digital camera in composing tone aspects of an image to be captured and/or later processed.